Vitamin D: What you need to know

Vitamin D

The form of vitamin D most talked about is the one known as Vitamin D3 or cholecalciferol, which is produced when the skin is exposed to sunshine.   Cholecalciferol is actually not a vitamin; it’s a prehormone which can be metabolized into a secosteroid hormone called calcitriol.  This hormone affects over 2000 genes or 10 percent of the human genome. That is probably why this "vitamin" affects the pathology of at least 17 varieties of cancer, as well as heart disease, stroke, hypertension, autoimmune disease, diabetes, depression, chronic pain, osteoarthritis, osteoporosis, muscle weakness, muscle wasting, birth defects, and periodontal disease among others.

Vitamin D Deficiency

When we are talking about vitamin D deficiency, we need to know what form of this vitamin we are referring to.  The correct form is 25-hydroxyvitamin D. That is why it’s a good idea to get a 25-hydroxyvitamin D test to determine whether you are vitamin D deficient.

According to Dr. John Cannell, president of vitamin D council, any serum level of 25-hydroxyvitamin D lower than 50 mg per ml in both children and adults should be considered vitamin D deficient. Many vitamin D experts recognize this level as the minimal acceptable level. At this level or lower, vitamin D cannot be stored in certain tissues of the body. In order to prevent many forms of diseases, 25-hydroxyvitamin D in the blood should fall into the range between 50 and 80 mg per ml year around.

Vitamin D3

Vitamin D3 is a form of vitamin D, which is chemically called cholecalciferol.  When we use the name vitamin D3, we often want to distinguish it from vitamin D2 or other forms of vitamin D.

Vitamin D Levels and Diseases

The status of your blood vitamin D3 or cholecalciferol can affect the risk for all types of diseases such as autism, cancer, depression, mental illness, and other ailments.

Although 50 mg per ml year round is considered adequate for healthy people, 75 mg per ml or higher levels may be needed to prevent cancer.  Be aware that more than 100 mg per ml may be too much for most people. Again we are talking about 25-hydroxyvitamin D.

Vitamin D Deficiency Symptoms

Chronic vitamin D deficiency may result in severe health conditions.  The outcomes are mere irritants; they can be major diseases. Bone pain and muscle weakness are two vitamin D deficiency symptoms.  Other conditions that may suggest vitamin D deficiency include high blood pressure, tuberculosis, depression, type 1 diabetes, periodontal disease, low blood calcium levels, chronic fatigue, bowed limbs, and a knock-kneed appearance.

Vitamin D Foods

While it is possible to get some vitamin D from your diet, dietary intake of even those foods high in vitamin D will not provide sufficient levels.

The best and safest way to get vitamin D is to get some sun.  At the hottest time of the day, exposing the hands and the face to sunlight for about 20 to 30 minutes can provide the maximum amount of the sunshine vitamin, which is 10,000 IU.

However, if sun exposure is out of the question, dietary supplements are in order. Experts suggest that adults can safely take 5000 IU per day; the very minimum you should obtain from a supplement is 1000 IUs.  

While it is difficult to obtain adequate levels of vitamin D in the foods we eat, there are a few food sources of the vitamin:  cod liver oil, herring, shiitake mushrooms, catfish, button mushrooms, pink salmon, sardines, canned mackerel, caviar, cow's milk, and egg yolk.

At this juncture, it is important to mention that vitamin A, which is found high in cod liver oil, can interfere with vitamin D absorption. 

Specifically, a high intake of vitamin A (active form) can actually reduce the efficacy of vitamin D.

Vitamin D and Cancer

There is no doubt that vitamin D can prevent many types of cancer. At this time, according to Dr. John Cannell, at least 17 types of cancer are known to be affected by vitamin D.  The only question that remains is how much vitamin D we need to prevent the disease.

Unfortunately we do not know exactly how much vitamin D we need to prevent cancer. One thing is certain: people with low levels of serum vitamin D are at a much higher risk of cancer.  Those who avoid sunshine may reduce their risk for skin cancers, but they are at higher risk for other types of more serious cancers.  A bit of vitamin D physiology may help you understand why high levels of serum vitamin D are needed to prevent or fight cancer.

There are three common forms of vitamin D, cholecalciferol (vitamin D3), calcidiol (25(OH)D3 or 25D3) and calcitriol(1,25(OH)2D3 or 1,25D3) in the human body.

Cholecalciferol is manufactured in large quantities in your skin when it is exposed to sunlight.  Of course, vitamin D3 is also obtainable from dietary supplements. 

Calcidiol (25-hydroxyvitamin D) is a prehormone directly made from cholecalciferol. This is the form that should be tested to determine whether you are vitamin D deficient.

Calcitriol (1,25-dihydroxyvitamin D) is a metabolic product formed from calcidiol in both the kidneys and in other tissues.  This is the most potent steroid hormone derived from vitamin D3 and it has powerful anticancer properties.

Now if you expose yourself to a good amount of sunshine, you can potentially make between 10,000 and 50,000 units of cholecalciferol in your skin, according to Dr. John Cannell.  That is why it is generally safe to take any dose of vitamin D3 or cholecalciferol that is lower than 10,000 units, which is actually the maximum level tolerable.

The good thing about the naturally occurring vitamin D is that you will never get too much of it by simply exposing yourselves to sunshine because once you make about 20,000 units, the ultraviolet that makes cholecalciferol begins to destroy some vitamin D3.

However, it is theoretically possible to experience vitamin D overdose when you ingest too much of dietary vitamin D supplements, even though in reality few cases of toxicity have been reported. That is because the dosages used by most people never reach the level that could lead to vitamin D toxicity.

After vitamin D3 is synthesized in the skin, it will be transported to the liver where it is metabolized into calcidiol or 25(OH)D, which some scientists believe has steroid hormone properties. Vitamin D is stored in the form of calcidiol.  When its level is below 40 mg per ml, vitamin D3 acts mostly to maintain the basic physiology such as maintenance of the normal blood calcium level.

When calcidiol reaches a certain level, it goes to the kidneys and other tissues. In the kidneys, calcidiol is transformed into calcitriol, the most potent steroid hormone in the human body that can turn on and off 2000 genes.  Obviously calcitriol is very important to health.  The most important role calcitriol plays may probably help regulate the blood level of calcium. When calcitriol is low, the blood calcium level falls and illness set in.

The anticancer properties of vitamin D may be seen only after calcidiol reaches tissues other than the liver and the kidneys.  When vitamin D3 or cholecalciferol is sufficient, calcidiol will reach other tissue and exhibit its anticancer properties. That is why high levels of vitamin D3 are needed to prevent cancer.

The amazing thing about this pathway encountered in other tissues is that the rate at which calcidiol is converted into calcitriol is not limited by the increased concentration of calcitriol. The more clacidiol you have in your blood, the more calcitriol you can have in cells.

Vitamin D Prostate Cancer

Low levels of vitamin D have been linked to high risk of prostate cancer and others.  Evidence has merged to suggest that taking high doses of vitamin D in the forms of calcidiol and calcitriol may help prevent or treat prostate cancer.  Receptors for vitamin D have been found in prostate cells, meaning that vitamin D plays a role in the physiology of prostate growth.  The only problem is that when high doses of calcidiol, or calcitriol, are used, high levels of calcium in the blood (hypercalcemia) may result. This is the same for treatment of other types of cancer using vitamin D3.  It remains unknown whether hypercalcemia would occur when cholecalciferol (vitamin D3) instead of calcidiol or clacitriol is used to treat cancer.

Vitamin D Autism

Autism is a disorder of the brain.  Vitamin D has been linked to autism through mainly two observations: vitamin D receptors (VDR) that are present in the brain tissue and low vitamin D levels in pregnant women were linked to impaired brain development in children. 

There is a direct association between the vitamin D receptors and the size of the brain as well.  Autistic children's brains are often larger than healthy children's.

Evidence is abundant to suggest that vitamin D may be implicated in the etiology of autism, even though not all people at the same serum level of vitamin D are at the same risk of autism. Certainly, more work needs to be done to understand the effect of vitamin D on autism.

Vitamin D Overdose

Overdosing on vitamin D is a problem with dietary supplements, although it is rare that people experience any toxicity with a dose lower than 10,000 units per day.  The maximal tolerable intake is 10,000 units per day.  The only thing that you should be aware of is that you should never use calcitriol, a highly potent steroid and prescription drug.

If exposure to sunshine is the way you get vitamin D, you would never have a problem like vitamin D overdose.

Vitamin D Sources

Vitamin D sources include exposure to sunshine, tanning beds, dietary supplements, foods high in vitamin D like salmon and other oily fish, and fortified foods and beverages like orange juice.

Vitamin D Supplements

When it comes to vitamin D supplements, it is generally recognized that vitamin D3 is the better form, even though some study suggests that vitamin D2 has similar effects.  In any case, you need to know that vitamin D in multivitamins is fairly low, often as low as 200 units, which is negligible.  Dr. John Cannell suggests that cod liver oil may not be a good vitamin D supplement because vitamin A levels in it are extremely high.  The individual vitamin D supplements may be the best route to take; there are many brands that provide 2000 units or 5000 units per pill or capsule.

For more information on vitamin D, visit vitamindcouncil.org 

By David Liu - davidl at foodconsumer dot org

Edited by Rachel Stockton - rachels at foodconsumer dot org